1. Field of the Invention
The present invention relates to a fuel supply control method and apparatus for an internal combustion engine.
2. Description of the Prior Art
In one known fuel supply control method, the engine running speed and the intake manifold pneumatic pressure are detected and then used to calculate the basic pulse width of an injection signal to be applied to the fuel injectors or to the fuel adjustment valves. This basic pulse width is corrected in accordance with the temperature of outer air introduced into the engine so as to compensate for deviation of the density of air in the intake manifold due to changes of the outer air temperature. The corrected pulse-width is used to adjust the actual fuel feed.
When the outer air temperature is high, the density of the air in the intake manifold decreases, although the intake manifold pneumatic pressure is constant. This causes the air-fuel ratio of the mixture introduced into combustion chambers to be rich relative to a stoichiometric condition. Contrary to this, when the outer air temperature is low, the density of the intake manifold air increases, causing the air-fuel ratio to be lean relative to a stoichiometric condition. Therefore, the fuel feed is corrected in accordance with the outer air temperature to compensate for deviation of the density of the intake manifold air and to control the air-fuel ratio to the stoichiometric condition.
However, according to the preceding system, since the air temperature is detected at an entrance of an air intake passage, the detected outer air temperature sometimes deviates from the actual temperature of air in the intake manifold. When the engine temperature varies, this deviation of the detected outer air temperature from the intake manifold air temperature increases particularly extremely. Thus, accurate correction of the air density cannot be executed.